311 research outputs found
Current Ripple Analysis of New Double-Stator AC Drive Systems
This paper presents a current ripple analysis of new double-stator AC drive system. At first, a new double-stator AC drive system is proposed. The aim is to combine the benefits both the multilevel and multiphase system to provide the better performance to drive AC motor. The input and output current ripples of the proposed AC drive system are then analyzed. The current ripples of the proposed AC drive system are then compared to the ones of conventional double-stator AC drive system. Under the same DC input voltage, it is shown that the proposed results in less output current ripple. Under the same output voltage, the proposed AC drive system results in smaller input current and, therefore, fewer losses on the DC power supply. Experimental results are included to show the validity of the proposed concept
Chandra Observations of SN 2004et and the X-ray Emission of Type IIp Supernovae
We report the X-ray detection of the Type II-plateau supernova SN 2004et in
the spiral galaxy NGC 6946, using the Chandra X-Ray Observatory. The position
of the X-ray source was found to agree with the optical position within ~0.4
arcsec. Chandra also surveyed the region before the 2004 event, finding no
X-ray emission at the location of the progenitor. For the post-explosion
observations, a total of 202, 151, and 158 photons were detected in three
pointings, each ~29 ks in length, on 2004 October 22, November 6, and December
3, respectively. The spectrum of the first observation is best fit by a thermal
model with a temperature of kT=1.3 keV and a line-of-sight absorption of
N_H=1.0 x 10^{22} cm^{-2}. The inferred unabsorbed luminosity (0.4-8 keV) is
~4x10^{38} erg/s, adopting a distance of 5.5 Mpc. A comparison between hard and
soft counts on the first and third epochs indicates a softening over this time,
although there is an insufficient number of photons to constrain the variation
of temperature and absorption by spectral fitting. We model the emission as
arising from the reverse shock region in the interaction between the supernova
ejecta and the progenitor wind. For a Type IIP supernova with an extended
progenitor, the cool shell formed at the time of shock wave breakout from the
star can affect the initial evolution of the interaction shell and the
absorption of radiation from the reverse shock. The observed spectral softening
might be due to decreasing shell absorption. We find a pre-supernova mass loss
rate of (2-2.5)x 10^{-6} M_{\odot} /yr for a wind velocity of 10 kms, which is
in line with expectations for a Type IIP supernova.Comment: total 19 pages including 7 figures. ApJ, in press. See
http://spider.ipac.caltech.edu/staff/rho/preprint/SN2004etms.ps for the paper
including full resolution image
Pharmacogenetics and Forensic Toxicology: A New Step towards a Multidisciplinary Approach
Pharmacogenetics analyzes the individual behavior of DNA genes after the administration
of a drug. Pharmacogenetic research has been implemented in recent years thanks to the improvement in genome sequencing techniques and molecular genetics. In addition to medical purposes,
pharmacogenetics can constitute an important tool for clarifying the interpretation of toxicological
data in post-mortem examinations, sometimes crucial for determining the cause and modality of
death. The purpose of this systematic literature review is not only to raise awareness among the
forensic community concerning pharmacogenetics, but also to provide a workflow for forensic toxicologists to follow in cases of unknown causes of death related to drug use/abuse. The scientific
community is called on to work hard in order to supply evidence in forensic practice, demonstrating that this investigation could become an essential tool both in civil and forensic contexts. The
following keywords were used for the search engine: (pharmacogenetics) AND (forensic toxicology);
(pharmacogenetics) AND (post-mortem); (pharmacogenetics) AND (forensic science); and (pharmacogenetics) AND (autopsy). A total of 125 articles were collected. Of these, 29 articles were included
in this systematic review. A total of 75% of the included studies were original articles (n = 21) and
25% were case reports (n = 7). A total of 78% (n = 22) of the studies involved deceased people for
whom a complete autopsy was performed, while 22% (n = 6) involved people in good health who
were given a drug with a subsequent pharmacogenetic study. The most studied drugs were opioids
(codeine, morphine, and methadone), followed by antidepressants (tricyclic antidepressants and
venlafaxine). Furthermore, all studies highlighted the importance of a pharmacogenetics study in
drug-related deaths, especially in cases of non-overdose of drugs of abuse. This study highlights the
importance of forensic pharmacogenetics, a field of toxicology still not fully understood, which is of
great help in cases of sudden death, deaths from overdose, deaths after the administration of a drug,
and also in cases of complaint of medical malpractice
Bulk synthesis of stoichiometric/meteoritic troilite (FeS) by high-temperature pyrite decomposition and pyrrhotite melting
Stoichiometric troilite (FeS) is a common phase in differentiated and undifferentiated meteorites. It is the endmember of the iron sulfide system. Troilite is important for investigating shock metamorphism in meteorites and studying spectral properties and space weathering of planetary bodies. Thus, obtaining coarse-grained meteoritic troilite in quantities is beneficial for these fields. The previous synthesis of troilite was achieved by pyrite or pyrrhotite heating treatments or chemical syntheses. However, most of these works lacked a visual characterization of the step by step process and the final product, the production of large quantities, and they were not readily advertised to planetary scientists or the meteoritical research community. Here, we illustrate a two-step heat treatment of pyrite to synthesize troilite. Pyrite powder was decomposed to pyrrhotite at 1023-1073 K for 4-6 h in Ar; the run product was then retrieved and reheated for 1 h at 1498-1598 K in N-2 (gas). The minerals were analyzed with a scanning electron microscope, X-ray diffraction (XRD) at room temperature, and in situ high-temperature XRD. The primary observation of synthesis from pyrrhotite to troilite is the shift of a major diffraction peak from similar to 43.2 degrees 2 theta to similar to 43.8 degrees 2 theta. Troilite spectra matched an XRD analysis of natural meteoritic troilite. Slight contamination of Fe was observed during cooling to troilite, and alumina crucibles locally reacted with troilite. The habitus and size of troilite crystals allowed us to store it as large grains rather than powder; 27 g of pyrite yielded 17 g of stochiometric troilite.Peer reviewe
23 GHz VLBI Observations of SN 2008ax
We report on phase-referenced 23 GHz Very-Long-Baseline-Interferometry (VLBI)
observations of the type IIb supernova SN 2008ax, made with the Very Long
Baseline Array (VLBA) on 2 April 2008 (33 days after explosion). These
observations resulted in a marginal detection of the supernova. The total flux
density recovered from our VLBI image is 0.80.3 mJy (one standard
deviation). As it appears, the structure may be interpreted as either a
core-jet or a double source. However, the supernova structure could be somewhat
confused with a possible close by noise peak. In such a case, the recovered
flux density would decrease to 0.480.12 mJy, compatible with the flux
densities measured with the VLA at epochs close in time to our VLBI
observations. The lowest average expansion velocities derived from our
observations are km s (case of a double
source) and km s (taking the weaker source
component as a spurious, close by, noise peak, which is the more likely
interpretation). These velocities are 7.3 and 2 times higher, respectively,
than the maximum ejecta velocity inferred from optical-line observations.Comment: 4 pages, 3 figures. Accepted in A&A on 24/03/200
Late-time observations of SN2006gy: Still Going Strong
Owing to its extremely high luminosity and long duration, SN2006gy radiated
more energy in visual light than any other known SN. Two hypotheses to explain
its high luminosity -- that it was powered by shock interaction with CSM as
implied by its Type IIn spectrum, or that it was fueled by radioactive decay
from a large mass of 56Ni synthesized in a pair-instability SN -- predicted
different late-time properties. Here we present observations of SN2006gy
obtained more than a year after discovery. We were unable to detect it at
visual wavelengths, but clear near-IR K and H-band detections show that it is
still at least as luminous as the peak of a normal SN II. We also present
spectra giving an upper limit to the late-time Ha luminosity of about 1e39
erg/s. Based on the weak late-time Ha, X-ray, and radio emission, combined with
the difficulty of explaining the shift to IR wavelengths, we can rule out
ongoing CSM interaction as the primary late-time power source. Instead, we
propose that the evolution of SN2006gy is consistent with one of two possible
scenarios: (1) A pair-instability SN plus modest CSM interaction, where the
radioactive decay luminosity shifts to the IR because of dust formation. (2) An
IR echo, where radiation emitted during peak luminosity heats a pre-existing
dust shell at radii near 1 light year, requiring the progenitor star to have
ejected another 10 Msun shell about 1500 yr before the SN.Comment: ApJ accepted. changes from prev version include more extensive
discussion of IR echo and implications, and new Fig
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